Conversion of Reactive Carbon Solutions into CO at Low Voltage and High Carbon Efficiency

Electrolyzers are now capable of reducing carbon dioxide (CO₂) into products at high reaction rates but are often characterized by low energy efficiencies and low CO₂ utilization efficiencies. We report here an electrolyzer that reduces 3.0 M KHCO₃(aq) into CO(g) at a high rate (partial current density for CO of 220 mA cm⁻²) and a CO₂ utilization efficiency of 40%, at a voltage of merely 2.3 V. These results were made possible by using: (i) a reactive carbon solution enriched in KHCO₃ as the feedstock instead of gaseous CO₂; (ii) a cation exchange membrane instead of an anion exchange membrane, which is common to the field; and (iii) the hydrogen oxidation reaction (HOR) at the anode instead of the oxygen evolution reaction (OER). The voltage reported here is the lowest reported for any CO₂ to CO electrolyzer that operates at high current densities (i.e., a partial current density for CO greater than 200 mA cm⁻²) with a CO₂ utilization efficiency of greater than 20%. This study highlights how the choice of feedstock, membrane, and anode chemistries affects the rate and efficiency at which CO₂ is converted into products.